The present invention is related to video surveillance, and in particular to a method and apparatus of controlling a plurality of video cameras to provide sufficient video quality on an as needed basis while maintaining relatively low bandwidth and storage requirement.
Video surveillance systems using Closed Circuit Television (CCTV) are commonly installed in office buildings, external structures, schools, and even on city streets. Video surveillance is becoming an integral component of access control methods augmented with biometrics, security tracking systems and access tracking systems.
Historically, CCTV systems were designed for point-to-point transmission of video from a camera to a recorder, and required a separate infrastructure that employed coaxial cable with analog video signals.
Recent developments include digital surveillance video and data networks. With digital surveillance video, the video from a surveillance camera is provided in digital form, e.g., in compressed form. With such developments, video surveillance systems can now operate over more flexible wiring such as local area networks (LANs), e.g., twisted pair LANs, and fiber optic cables using protocols including TCP/IP, UDP, and RTP. The surveillance video streams are encoded and then stored in a digital format on a server or other computer hard drive as opposed to videotape such as analog videotape. This new breed of digital video surveillance systems allow IP (Internet Protocol) transmission of the video signals as a video stream, or as a combined voice/video stream that can be viewed remotely in real time, or stored for later review.
Video compression provides for efficiently transmitting and storing the video from a set of surveillance cameras. Video compression can either be carried out locally close to the video camera or can be carried out at a central location where the compressed video is stored. Known video compression formats that are used in modern digital video surveillance systems include: MPEG-1, MPEG-2, MPEG-4, H.261, H.263, and motion JPEG (MJPEG).
So-called digital surveillance cameras compress the video stream locally close-to or in the camera. Such a camera and encoder is called a surveillance camera/encoder combination herein. Thus, in one typical modern digital video surveillance system in which compression is carried out locally in a surveillance camera/encoder combination, the video captured from each surveillance camera in a surveillance camera/encoder combination is digitized and locally encoded by an encoder in the surveillance camera/encoder combination into a compressed video stream that has a constant bit rate. Each compressed video stream from a plurality of such surveillance camera/encoder combinations is sent to a central location for monitoring and storage. In such a system, each surveillance camera/encoder combination's encoder encodes the captured video independently at a pre-determined, e.g., constant bit rate if some of the cameras are in the same general region. The overall bandwidth (total bit rate that can be accommodated) for the plurality of surveillance camera/encoder combinations determines the pre-defined bit rate of each surveillance camera/encoder combination such that all surveillance camera/encoder combinations may be accommodated in the allocated bandwidth. In such a system, for any viewed location that is relatively quiet, e.g., where there is little or no activity, the surveillance camera/encoder combination's encoder provides the pre-defined bit rate by carrying out bit-stuffing. If there is little or no activity in all the cameras, each surveillance camera/encoder combination's encoder performs the bit-stuffing. On the other hand, if there is simultaneously a high level of activity in all or most of the surveillance camera/encoder combinations, the constant pre-determined bit rate may not be sufficient to provide adequate video quality at least from some of the surveillance camera/encoder combinations. That is, in order not to waste too much bandwidth during such time—typically most of the time—when there is relatively little or no activity, a compromise is typically made in determining the pre-defined bit rate such that the bit rate is too low to provide adequate video quality on some scenes when there is activity. On the other hand, if the constant bit rate is set so that adequate quality is provided, there typically is a waste of bandwidth for those times—typically most of the time—when there is no activity.
Thus there is a need in the art for a method and apparatus of controlling a plurality of surveillance camera/encoder combinations that each provide a constant bit rate, the controlling configured to provide adequate view quality at critical times to not be wasteful of bandwidth at other times.
One prior art method is to control the bit rates of the surveillance camera/encoder combinations based on operator desire or other metrics as decided by the user of the equipment. One version includes the time of day as a metric, such that for a particular camera/encoder combination, the bit rate of the compressed video from the particular camera/encoder combination is relatively low at times of the day where there is less likely to be activity and higher for another time of day when there is a higher likelihood of activity in the scene viewed by the camera/encoder combination. Another version includes the amount of light, such that for a particular surveillance camera/encoder combination, the bit rate of the compressed video from the particular surveillance camera/encoder combination is relatively low when the lighting is relatively good.